This application relates to radiology and radiotherapy, and is more particularly directed to imaging devices for aligning and monitoring a treatment radiation field relative to a patient positioned on a treatment table.
Radiation therapy involves applying one or more doses per treatment of high-energy x-ray radiation to a patient. The strength of the radiation must be concentrated in a specific area, e.g. to control a tumor, but the total radiation to which the patient is subjected should be kept low as possible. It is the current practice, prior to radiation therapy, for the patient to be positioned on a simulator, that is, on a low-energy x-ray machine which is otherwise identical to the x-ray treatment machine. An x-ray image is exposed onto film at the simulator, and this simulator image shows a portion of the patients body which is to receive radiation treatment. Then, using the information obtained on the simulator, the oncologist can prescribe the appropriate dosage, and can outline how the treatment field is to be collimated. However, the collimation of the field is always an approximate measure, because the patient can never be positioned exactly the same on the therapy machine as on the simulator. Also, there is always some movement of the patient's internal tissues between simulator and treatment, and, for that matter, during treatment. This means that the prescribed dose must be applied to a greater area than the tumor, and this subjects much of the surrounding tissues to radiation.
Prior attempts to use the radiation from a treatment machine to produce images have resulted in low resolution and poor contrast response. Prior to this invention, a cassette film device had to used for therapy imaging which was inconvenient, requried labor and time to develop the film, and yielded poor image quality.
Because the images are of low quality, the inconvenience to use and the time required to monitor the position of the applied dosage field to develop the film the cassette film device is not widely used to align the therapy beam relative to the patient.
During set up of the treatment machine, there are normally several people, namely the patient, oncologist, and at least one technologist in the room around the treatment table. A video fluoroscopic device mounted on the gantry below the table would be in the way of the practitioners. However, if the device were not affixed onto the gantry, it would be difficult or impossible to align the device precisely with the treatment beam.